1. Field of the Invention
The present invention relates to a speed and phase controller for a motor, and more particularly, to a motor speed and phase controller for a video cassette recorder (VCR).
2. Discussion of the Related Art
The operation of a conventional motor speed and phase controller will now be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic diagram of a conventional motor controller in a general VCR, which includes a speed detector 1 and a phase detector 2 for respectively detecting speed and phase of a rotating motor M, a speed servo 3 and a phase servo 4 for respectively comparing the speed and the phase respectively detected by speed detector 1 and phase detector 2 and each outputting a signal corresponding to a difference between the detected value and a target value, a speed gain controller 5 and a phase gain controller 6 for processing the signals output from speed servo 3 and phase servo 4 by a gain fixed during the designing process, a motor driving controller 7 for receiving output signals of speed gain controller 5 and phase gain controller 6 and controlling the same by a final gain value to output a pulse-width modulated (PWM) signal and outputting a motor-on signal (ON) and a forward/reverse determination signal (F/R), a lowpass filter (LPF) 8 for converting the PWM signal output from motor driving controller 7 into a DC signal, a DC/DC converter 9 for converting the signal output from LPF 8 into an actual motor driving power supply (V.sub.s), and a driver 10 for driving motor M in a playback mode by the signal output from DC/DC converter 9, for receiving a stand-by signal, i.e., the motor-on signal (ON) and forward/reverse determination signal (F/R) and for driving motor M in a still picture mode. Here, speed servo 3 and phase servo 4, speed gain controller 5 and phase gain controller 6, and motor driving controller 7 are software operated, and LPF 8, DC/DC converter 9 and driver 10 are hardwired.
The operation of the conventional motor controller having the aforementioned configuration will now be described.
In the case of playback operation, the speed and phase are detected by speed detector 1 and phase detector 2, respectively to control motor M to be suitable for the playback mode to reach a target speed and a target phase. The detected speed and phase are compared with the target speed and target phase in speed servo 3 and phase servo 4 which output error signals corresponding to the difference between detected and target values.
The output error signal is processed by a gain control value set by speed gain controller 5 and phase gain controller 6 determined by the design and is added to speed and phase signal to then be input to motor driving controller 7.
Then, motor driving controller 7 gain-controls the signal to be suitable for the playback mode once again to then output a final control signal, i.e, the PWM signal with a changed on-time period. The output PWM signal is converted into a DC signal in LPF 8 and converted into an actual motor driving power supply in DC/DC converter 9 for application to driver 10, thereby controlling motor M.
In the case of a still picture implementation, if a picture is input during the playback mode, the speed and phase are detected by speed detector 1 and phase detector 2, respectively to control motor M driven at a target speed and phase during the current playback mode in accordance with the still picture mode. The detected speed and phase are compared with the target speed and target phase in speed servo 3 and phase servo 4 to output an error signal corresponding to the difference between the detected and target values.
The output error signal is processed by a gain control value set by speed gain controller 5 and phase gain controller 6 and is added to the speed and phase signals to then be input to motor driving controller 7.
Then, motor driving controller 7 outputs a still picture mode stand-by signal, i.e., the motor-on signal (ON) and forward/reverse determination signal (F/R) to driver 10 in order to stop motor M driven by the PWM signal being generated in the current playback mode, thereby controlling motor M.
The process of controlling the still picture will be described with reference to FIGS. 2a to 2d.
As shown in FIG. 2a, if a still picture signal is input during a playback mode, motor driving controller 7 detects the playback phase inclined forward and backward when a video head traces a video track of a tape to stop the driving of motor M to then determine time t.sub.1. Then, in a time t.sub.1 from a head switching time, controlling is performed for a predetermined motor brake period t.sub.2 using the forward/reverse rotation determining signal (F/R) of motor M (FIG. 2c) and the motor driving power supply (V.sub.s) which is a motor control signal (FIG. 2d).
Here, the control time t.sub.1 at stop is increased if the current video head VH lags the tape video track, and is decreased if the current video head VH leads the tape video track, thereby implementing a still picture.
However, the conventional technologies consider only the speed and phase relationship between the current video head and tape video track to realize the motor speed and phase control in order to control a motor. Actual usage conditions (i.e., tape difference according to time, tape difference according to its initial, middle, and terminal periods, tape travelling load difference according to mechanism, and load changes applied to the mechanism and tape) are not considered. Therefore, when a user selects a still picture mode or a playback mode, the motor is only sensitive to surrounding conditions and is not optimally controlled according to the load on the motor. Consequently, a high definition picture is not obtained.